It is disturbing to see a far-right mob rampage through the streets of any city but, for obvious historical reasons, the scene is uniquely distressing in Germany. In Chemnitz, in the state of Saxony, extremists this week rallied in such numbers that police seemed unable – or, some suspect, unwilling – to prevent indiscriminate racist violence.

The ostensible trigger was the stabbing of a German man, allegedly by assailants of Syrian and Iraqi origin. But, as Michael Kretschmer, Saxony’s state premier, observed, extremists used the crime as an instrument of mass mobilisation. They mustered thousands of supporters, drawing in recruits from across Germany. Mr Kretschmer looked bewildered by events, reflecting a wider disorientation in his Christian Democratic Union party. The CDU once had a solid grip on Saxony but its position has slipped to the benefit of the far-right Alternative für Deutschland. The Afd is expected to do well in state elections next year and has been inflaming tensions around Chemnitz, practically inciting a pogrom. One of its MPs has spoken on social media about the public duty to stop “knife migration”. Another wrote of “brave citizens of Chemnitz” protesting against “criminal Muslim migrants”.

The CDU seems paralysed by the rise of the AfD, which did well enough in federal elections last year to force Angela Merkel into a fragile coalition with the Social Democratic party – the second pillar of the country’s party political establishment. That makes the far-right the main opposition in parliament. This is the flowering of something dangerous, with deep roots.

In tracing the cause of Mrs Merkel’s woes, it is common to cite her embrace of an open asylum policy during the 2015 refugee crisis. She was celebrated as a hero by liberals abroad, and many Germans responded with admirable generosity. But compassion fatigue set in, while xenophobes stoked suspicion that the nation’s hospitality was being abused by terrorists and bandits. Mrs Merkel was burned by the experience and the pain was contagious. Many German politicians seem to have lost their collective voice when it comes to the defence of migration, although many employers in the country say they need to import skilled labour to fill vacancies.

But the far-right threat in Germany obviously predates Mrs Merkel’s humane gesture. It is most severe in areas of the former German Democratic Republic, which still bears the scars of economic dysfunction as a Soviet satellite and of rapid deindustrialisation when the two Germanies were united. In terms of cultural marginalisation, Saxony is seen as the easternmost part of the left-behind east.

The GDR regime stored up economic problems that reunification hasn’t solved. It also incubated tolerance of totalitarian ideas. The communist authorities celebrated Nazism’s defeat but never repaired civic bonds and democratic institutions. The east did not undergo the traumatic but essential self-examination that racked West Germany in the generation after the second world war. Its politics were not coloured by an ethos of atonement in the same way. That omission is now being felt in a lowered immunity to fascism.

Immunity is down across Europe, and a generation of technocrats who imagined that politics could be a perpetual alternation between centre-left and centre-right look ill-equipped for the challenge. Mrs Merkel has been a paragon of stability and a powerful advocate of principled moderation in domestic and international arenas, but there is not an obvious “Merkelist” movement ready to step in when she stands down. Germany is not alone in lacking dynamic, liberal politicians who have the confidence and the arguments to cut through the thickening miasma of far-right resurgence.

Earlier this year, Mrs Merkel said: “When the generation that survived the war is no longer with us, we’ll find out whether we have learned from history.” It sounded strangely fatalistic from a politician in the twilight of her power. But really it was a challenge to the present generation and the one now rising: to prove that those lessons from history are unforgotten.